Method and system of tape automated bonding

ABSTRACT

A tape automated bonding (TAB) structure which includes a flex tape having a conductive lead pattern formed thereon. The conductive lead pattern includes a plurality of leads configured to form an inner lead bond (ILB) portion of the TAB structure. At least one of the plurality of leads is internally routed and has a contact exposed interior to the ILB portion of the TAB structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 09/970,145,filed on Oct. 2, 2001, now U.S. Pat. No. 7,190,069, which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of integrated circuit packaging andmore specifically to a method and system of tape automated bonding foran integrated circuit for an implantable medical device such as adefibrillator, pacemaker, or cardioverter.

BACKGROUND

Patients prone to irregular and sometimes life threatening heart rhythmssometimes have miniature defibrillators, cardioverters, and pacemakersimplanted in their bodies, typically in the upper chest area above theirhearts. These devices detect onset of abnormal heart rhythms andautomatically apply corrective electrical therapy, specifically one ormore bursts of electric current, to hearts. When the bursts of electriccurrent are properly sized and timed, they restore normal heart functionwithout human intervention, sparing patients considerable discomfort andoften saving their lives.

The devices include a set of electrical leads, which extend from ahousing into a heart after implantation. Within the housing, among othercomponents, is electronic circuitry for detecting abnormal heart rhythmsand for controlling the bursts of electric current through the leads tothe heart. The electronic circuitry includes integrated circuits (ICs)which are mounted to a circuit board and connected to various otherdiscrete electrical components by electrically conductive conduitsbetween input/outputs (I/O's) of the IC and the various discreteelectrical components.

One method of mounting the IC to the circuit board and providing theinterconnections between the IC and the discrete components includestape automated bonding (TAB). In TAB, interconnection leads arepatterned on a flex tape. The tape is positioned above the bare IC chipso that the metal tracks on the tape correspond to I/O bonding sites onthe perimeter of the chip. An outer portion of the TAB leads are thenconnected to contacts on the circuit board. The circuit board includesleads running from the contacts to the discrete electrical components.Since the implantable devices are typically implanted in the left regionof the chest or in the abdomen, a smaller size device, which is stillcapable of performing complex cardiac rhythm management schemes, isdesirable.

Accordingly, there is a need to provide a compact implantable devicewhich is capable of performing complex cardiac rhythm managementschemes. Furthermore, there is a need to provide methods ofmanufacturing devices and assembling structures such as the ICs withinthe implantable devices that provide more efficient and thus lessexpensive manufacturing.

SUMMARY

To address these and other needs, methods and systems for tape automatedbonding have been devised. One aspect of the present system includes aTAB structure. In one embodiment, a TAB structure includes a tape havinga conductive lead pattern formed thereon, wherein the conductive leadpattern includes a plurality of leads configured to form an inner leadbond (ILB) portion of the TAB structure. At least one of the pluralityof leads is internally routed relative to the ILB portion and has acontact exposed interior to the ILB portion of the TAB structure.

One aspect of the present system includes an electrical device. In oneembodiment, an electrical device includes a circuit board, an IC chipmounted to the circuit board, and an electrical component mounted abovethe IC chip and electrically connected to the IC chip via a leadextending from the electrical component to an I/O of the IC chip.

One aspect includes a method of interconnecting an IC chip to anelectronic component. In one embodiment, a method includes connectingthe IC to a TAB tape at an ILB portion of the TAB tape and connectingdiscrete components to one or more leads of the TAB tape at internalportions of the TAB tape within the ILB portion and above the IC chip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a TAB structure according to one embodiment.

FIG. 2 shows a sectional side view of the TAB structure of FIG. 1.

FIG. 3 is an isometric view of the TAB structure of FIG. 1 havingelectrical components mounted thereto.

FIG. 4 shows a top view of a TAB structure according to one embodiment.

FIG. 5 shows an isometric view of the TAB structure of FIG. 4 havingelectrical components mounted thereto.

FIG. 6 shows a block diagram of a generic implantable device includingan electrical circuit in accordance with one embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments in which the invention may bepracticed. It is understood that other embodiments may be utilized andstructural changes may be made without departing from the scope of thepresent invention.

The increases in density that have occurred within ICs have made itpossible to provide more functions in each IC, such as more logic gatesor more memory bits. This increase in function has made it necessary inmany cases to provide more interconnections per IC chip. IC chips havealso grown in size to accommodate the larger number of individualcircuits, gates or bits required for the expanded functions. The presentsystem and method offers a technique of redistributing the I/Ointerconnections of an integrated circuit. In one example, a TABleadframe is utilized to embody the technique.

FIGS. 1-3 show a TAB structure 100 according to one embodiment. FIG. 1shows a top view of TAB structure 100. TAB structure 100 is one of aplurality of similar TAB lead-frame structures that are located in aseries along a sprocketed tape 110. Each TAB structure 100 includes tape110, such as polyimide or other flex tape, having a conductive leadpattern 120 formed thereon. The TAB structure 100 provides the necessaryconnections for the perimeter bonded I/Os of an unpackaged or bare ICchip 126.

IC 126 includes a plurality of IO contact pads 202 (See FIG. 2) forproviding coupling of the IC to outside components. The I/O contact padscan be located all around the perimeter circumference of a surface ofthe IC. By way of example, there can be anywhere from approximately 16to 500 I/O contact pads or more on the chip. IC 126 can be a square ornon-square rectangular chip.

In one embodiment, the conductive lead pattern 120 includes a copperetched and gold plated metallization on tape 110. In one example, informing TAB structure 100, a conductor layer composed of Cu or the likeis formed on a tape 110 composed of a material such as a polyimide tapeor other flex tape. Thereafter, the conductor layer is etched out andthereby a conductive lead pattern is formed.

Conductive lead pattern 120 includes a plurality of leads 123. The leads123 of conductive lead pattern 120 include an inner lead bond (ILB)portion 122 and an outer lead bond (OLB) portion 124. One or more of theIC chip I/O contact pads 202 connect to the one or more of leads 123 atthe ILB portion 122 when the IC chip is mounted within an inner framesection 128 of TAB 100. The inner frame section 128 is dimensioned tohold IC 126 chip therein. OLB portion 124 is for connecting the IC chipto a circuit board, for example. Accordingly, a conductive path isformed from the ILB portion 122 at the I/O of the IC to the OLB portion124 which is connected to a circuit board.

One or more of the plurality of leads 123 of TAB structure 100 includesinternally located contacts 132. Contacts 132 are located within framesection 128 and are connected interiorly relative to ILB portion 122.Among other advantages, this allows one or more components to be mountedon or above the surface of the IC and thus within the perimeter of theIC, thus not using up any more footprint area upon a circuit board. Inone example, the internally running leads are formed in the same manneralong with the rest of lead pattern 120. Since TAB leadframe cost isrelatively constant even with added complexity, the present system doesnot cause any significant incremental cost to manufacturing or assemblyof the TAB.

In one embodiment, a plurality of test contact pads 127 are located onthe TAB structure and are connected to one or more of leads 123. Forexample, FIG. 1 shows example leads 123 b connected to test contact pads127. In some embodiments, each of the plurality of leads 123 areconnected to test contact pads. Other embodiments only connect one ormore of leads 123 to contact test pads. The present example is shown forsake of clarity. The present TAB structure having test contact pads 127allows for “known-good-die” testing. Known-good-die testing iselectrical testing or bum-in of the integrated circuit prior tocommitting the expensive discrete components to the overall electricalassembly. Accordingly, in one example use of the present TAB system,once the ILB TAB bonds are completed, the IC 126 can be electricallytested using test contact pads 127 to verify that the circuit is stableand capable of meeting the rigors and high quality standards needed ofan implantable defibrillator or pacemaker or other implantable device.The present embodiment accommodates known-good-die testing while stilloptimizing the surface area utilization above the IC in the form ofactive circuitry. This results in a smaller, more comfortable, and morereliable implantable device. Moreover, the present structure allows thepackaging designer to optimize the circuit board or hybrid surface areawhich helps to minimize overall device volume while still allowing forcomplex electronic functions.

One advantage of the present structure is that it allows for reductionsin electrical impedance between the IC and the associated discreteelectrical components due to the very short and direct connectionsbetween the IC and the components mounted above the IC. The structurealso reduces the number of electrically redundant interconnects betweenthe IC, the components above the chip, and the hybrid (motherboard) byutilizing a continuous stitch TAB inner lead bond approach to make thenecessary electrical connections. In the past, the IC was connected tothe hybrid, such as a circuit board, and then a lead went from thehybrid to the component. Now a component can utilize the TAB lead itselfas the component's direct interconnect.

Moreover, the present internal contacts 132 allow for lower cost andless complex manufacturing. This is because the internal contacts 132allow a component to be mounted with a one-step manufacturing process tothe IC. A typical two-step process of first mounting the component tothe circuit board and then connecting the component to the IC is reducedto mounting the component directly within the frame of the TAB structurewith its built-in connection.

FIG. 2 shows a schematic representation of a cross-section of portionsof TAB structure 100. In this embodiment, example lead 123D extends froma test contact pad 127 to OLB portion 124 to ILB portion 122 and toinner contact 132 located above the major surface of chip 126. In thisexample, a conductive filler material 133 is used to make the connectionbetween lead 123D and inner contact 132.

Chip 126 includes I/O contact 202 for making the connection to the lead.In other examples a lead such as lead 123D can extend only inward, forexample, from ILB 122 to contact 132. Other leads extend only outward,for example, from ILB 122 to OLB 124.

FIG. 3 is an isometric view of TAB structure 100 having electricalcomponents, such as components 302, 304, 306, and 307, mounted thereto.In this example, ILB portions 122 are connected to the I/Os of chip 126and OLD portions 124 have been bent into a gull-wing configuration inpreparation for mounting onto a circuit board. An example lead 123C runsfrom IC I/O 202 to inner contact 132. Components 302, 304, 306, and 307can be soldered to contacts 132. Alternatively they can be connected byan electrically conductive epoxy. Other equivalent connection techniquesare within the scope of the present system.

FIGS. 4 and 5 show a TAB structure 400 according to one embodiment. FIG.4 shows an isometric view of TAB structure 400. Tab structure 400includes similar features to TAB structure 100 and certain details willbe omitted for sake of clarity. TAB structure 400 generally includes atape 410 having a conductive lead pattern 420 formed thereon. Conductivelead pattern 420 includes a plurality of leads 423. The leads 423 ofconductive lead pattern 420 include an ILB portion 422 and an OLBportion 424.

One or more of the plurality of leads 423 of TAB structure 400 includesinternally located contacts 432. Contacts 432 are located within framesection 438 and are connected interiorly relative to ILB portion 422.This allows one or more components to be mounted above the surface of anIC and thus within the perimeter of the IC, thus not using up any morefootprint area upon a circuit board.

In one embodiment, TAB structure 400 includes internally locatedcontacts 425. In this example, inner contacts 425 do not include contactpads such as provided for inner contacts 432. Inner contacts 425 includea bare portion of portions of each of one or more of leads 423 and areinternally located relative to ILB portion 422. Again, inner contacts425 allow one or more components to be mounted above the surface of theIC and within the perimeter of the IC, thus not using up any morefootprint area upon a circuit board.

FIG. 5 is an isometric view of TAB structure 400 having an IC chip 526mounted thereto and having electrical components, such as components502, 504, 506 and so on, mounted thereto. ILB portions 422 are connectedto the I/Os 528 of chip 526 and OLB portions 424 have been bent into agull-wing configuration in preparation for mounting onto a circuit board532. In this example, lead 423D is attached to an I/O 528 of IC 526. Oneend of lead 423D extends to OLB portion 424 and a second end extends toan inner contact 432 (see FIG. 4), which in FIG. 5 has a component 504mounted thereon. Again, the present TAB structure provides thatcomponents such as component 504 do not take up any space on the surfaceof the circuit board.

This example also shows a lead 423E connected to an I/O 528 of the IC.Lead 423E includes a first end extending to OLB portion 424 and a secondend extending internally to inner contact 425, where inner contact 425is attached to the I/Os of component 506. In this example, component 506is an IC chip having similar I/Os as shown for IC chip 526. Thus, thepresent embodiment allows the back-to-back, internally located mountingof a second IC chip 506 relative to a first IC chip 526.

FIG. 6 shows one of the many applications for circuit boardsincorporating one or more teachings of the present TAB system: a genericimplantable device 600. As used herein, implantable device includes animplantable device for providing therapeutic stimulus to a heart muscle.Thus, for example, the term includes pacemakers, defibrillators,cardioverters, congestive heart failure devices, and combinations ofthese devices.

Device 600 includes a lead system 603, which after implantationelectrically contacts strategic portions of a patient's heart. Shownschematically are portions of device 600 including electrical circuitrysuch as a monitoring circuit 602 for monitoring heart activity and fordetecting abnormal heart rhythms through one or more of the leads oflead system 603, and a therapy circuit 601 for controlling anddelivering bursts of electrical energy through one or more of the leadsto a heart. Device 600 also includes an energy storage component, whichincludes a battery 604 and a capacitor 605. Therapy circuit 601 andmonitoring circuit 602 can both include circuit boards or hybrids havingelectrical devices which include one or more of the TAB featuresdescribed above. In one example, the electrical circuitry of device 600includes application-specific integrated circuits (ASICs) to monitor,regulate, and control the delivery of electrical impulses to the heart.The present TAB structure allows a packaging designer to increase hybridefficiency by turning the otherwise passive IC surface into anelectrically active design element and therefore offering a significantreduction in the size of implantable device 600.

It is understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A tape automated bonding (TAB) structure for connecting a chip havingone or more perimeter I/Os to a circuit board, the TAB structurecomprising: a TAB flex tape having a conductive lead pattern formedthereon, the conductive lead pattern including a plurality of leadsconfigured to form an inner lead bond (ILB) area to connect to the oneor more perimeter I/Os of the chip and an outer lead bond (OLB) area toconnect to the circuit board, wherein at least one of the plurality ofleads is internally routed relative to the ILB area so that the at leastone lead has a contact exposed interior to the ILB portion of the TABstructure such that the at least one lead is configured to extend from aperimeter I/O of the chip inward to an electronic component mounted overthe chip.
 2. The TAB structure of claim 1, wherein the contact ispositioned for mounting a discrete electrical component on or above amajor surface of the chip.
 3. The TAB structure of claim 1, wherein atleast one of the plurality of leads is connected to a test contact pad.4. The TAB structure of claim 1, wherein the ILB area has a generallyrectangular shape.
 5. The TAB structure of claim 1, wherein the OLB areahas a generally rectangular shape.
 6. The TAB structure of claim 1,wherein the TAB flex tape is a polyimide tape.
 7. A tape automatedbonding (TAB) structure for connecting a chip having one or moreperimeter I/Os to a circuit board, the TAB structure comprising: a TABflex tape having a conductive lead pattern formed thereon, theconductive lead pattern including a plurality of leads configured toform an inner lead bond (ILB) area to connect to the one or moreperimeter I/Os of the chip and an outer lead bond (OLB) area to connectto the circuit board, wherein at least one of the plurality of leads isinternally routed relative to the ILB area so that the at least one leadhas a contact exposed interior to the ILB portion of the TAB structureto connect to an electrical component located on or above a surface ofthe chip, wherein the internally routed lead extends from a point whichis within the ILB area of the TAB structure outward toward the OLB areaof the TAB structure such that the internally routed lead is configuredto extend from the electrical component to a perimeter I/O of the chipwhen the electrical component is mounted on or over the chip.
 8. The TABstructure of claim 7, wherein at least one of the plurality of leads isconnected to a test contact pad.
 9. The TAB structure of claim 7,wherein the ILB area has a generally rectangular shape.
 10. The TABstructure of claim 7, wherein the OLB area has a generally rectangularshape.
 11. The TAB structure of claim 7, wherein the TAB flex tape is apolyimide tape.
 12. A tape automated bonding (TAB) structure forconnecting a chip having one or more perimeter I/Os to a circuit board,the TAB structure comprising: a TAB flex tape having a conductive leadpattern formed thereon, the conductive lead pattern including aplurality of leads configured to form a generally rectangular inner leadbond (ILB) area to connect to the one or more perimeter I/Os of the chipand a generally rectangular outer lead bond (OLB) area to connect to thecircuit board, wherein at least one of the plurality of leads isinternally routed relative to the ILB area so that the at least one leadhas a contact exposed interior to the ILB portion of the TAB structureand above a major surface of the IC chip to connect to an electricalcomponent located on or above a surface of the IC chip, wherein theinternally routed lead extends from a point which is within an innerportion of the TAB structure outward toward an outer portion of the TABstructure such that the lead is configured to extend from the electricalcomponent to a perimeter I/O of the IC chip when the electricalcomponent is mounted on or over the chip.
 13. The TAB structure of claim12, wherein at least one of the plurality of leads is connected to atest contact pad.
 14. The TAB structure of claim 12, wherein the TABflex tape is a polyimide tape.